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論文

Elastic properties of nuclear pasta in a fully three-dimensional geometry

Xia, C.-J.*; 丸山 敏毅; 安武 伸俊*; 巽 敏隆*; Zhang, Y.-X.*

Physics Letters B, 839, p.137769_1 - 137769_5, 2023/04

 被引用回数:1 パーセンタイル:70.47(Astronomy & Astrophysics)

Realistic estimations on the elastic properties of neutron star matter are carried out with a large strain ($$varepsilon$$ $$_sim^{<}$$ 0.5) in the framework of relativistic-mean-field model with Thomas-Fermi approximation, where various crystalline configurations are considered in a fully three-dimensional geometry with reflection symmetry. Our calculation confirms the validity of assuming Coulomb crystals for the droplet phase above neutron drip density, which nonetheless does not work at large densities since the elastic constants are found to be decreasing after reaching their peaks. Similarly, the analytic formulae derived in the incompressible liquid-drop model give excellent description for the rod phase at small densities, which overestimates the elastic constants at larger densities. For slabs, due to the negligence on the variations of their thicknesses, the analytic formulae from liquid-drop model agree qualitatively but not quantitatively with our numerical estimations. By fitting to the numerical results, these analytic formulae are improved by introducing dampening factors. The impacts of nuclear symmetry energy are examined adopting two parameter sets, corresponding to the slope of symmetry energy L = 41.34 and 89.39 MeV. Even with the uncertainties caused by the anisotropy in polycrystallines, the elastic properties of neutron star matter obtained with L = 41.34 and 89.39 MeV are distinctively different, results in detectable differences in various neutron star activities.

論文

Nuclear pasta structures at high temperatures

Xia, C.-J.*; 丸山 敏毅; 安武 伸俊*; 巽 敏隆*

Physical Review D, 106(6), p.063020_1 - 063020_14, 2022/09

 被引用回数:3 パーセンタイル:52.13(Astronomy & Astrophysics)

We study nuclear pasta structures at high temperatures within a relativistic mean field model and Thomas-Fermi approximation. Typical structures (droplet, rod, slab, tube, and bubble) are obtained, which form various crystalline configurations. The properties of those nuclear pastas are examined in a three-dimensional geometry with reflection symmetry, where the optimum lattice constants are fixed minimizing the free energy under spherical or cylindrical approximations for Wigner-Seitz cells. For fixed densities and temperatures, the differences of the free energies per baryon for various shapes and lattice structures are typically on the order of tens of keV, suggesting the coexistence of those structures. If we further increase temperature, eventually the non-uniform structures of nuclear pasta become unstable and are converted into uniform nuclear matter. The phase diagrams of nuclear matter are estimated, which is useful for understanding the various phenomena in neutron stars.

論文

Kaon-baryon coupling schemes and kaon condensation in hyperon-mixed matter

武藤 巧*; 丸山 敏毅; 巽 敏隆*

Progress of Theoretical and Experimental Physics (Internet), 2022(9), p.093D03_1 - 093D03_37, 2022/09

 被引用回数:0 パーセンタイル:0.01(Physics, Multidisciplinary)

The possible coexistence of kaon condensation and hyperons in highly dense matter is investigated. Two coupling schemes for the s-wave kaon-baryon interaction are compared regarding the onset density of kaon condensation in hyperon-mixed matter and the equation of state for the developed ($$Y+K$$) phase. One is the contact interaction scheme related to the non-linear effective chiral Lagrangian. The other is the meson exchange scheme. It is shown that in the meson exchange scheme, the contribution from the non-linear scalar self-interaction gives rise to a repulsive effect for the kaon effective energy, pushing up the onset density of kaon condensation. The non-linear self-interacting term is not relevant to repulsive energy leading to stiffening of the EOS at high densities, and it cannot be compensated with a large attractive energy due to the appearance of the ($$Y+K$$) phase in the case of the contact interaction scheme.

論文

Sodium-cooled Fast Reactors

大島 宏之; 森下 正樹*; 相澤 康介; 安藤 勝訓; 芦田 貴志; 近澤 佳隆; 堂田 哲広; 江沼 康弘; 江連 俊樹; 深野 義隆; et al.

Sodium-cooled Fast Reactors; JSME Series in Thermal and Nuclear Power Generation, Vol.3, 631 Pages, 2022/07

ナトリウム冷却高速炉(SFR: Sodium-cooled Fast Reactor)の歴史や、利点、課題を踏まえた安全性、設計、運用、メンテナンスなどについて解説する。AIを利用した設計手法など、SFRの実用化に向けた設計や研究開発についても述べる。

論文

A Bag model of matter condensed by the strong interaction

Miao, Z.-Q.*; Xia, C.-J.*; Lai, X.-Y.*; 丸山 敏毅; Xu, R.-X.*; Zhou, E.-P.*

International Journal of Modern Physics E, 31(4), p.2250037_1 - 2250037_20, 2022/04

 被引用回数:5 パーセンタイル:83.8(Physics, Nuclear)

It is suggested that pulsar-like compact stars are comprised entirely of strangeons (quark-clusters with three-light-flavor symmetry) and a small amount of electrons. To constrain the properties of strangeon stars, we propose a linked bag model to describe matter with the strong interaction in both 2-flavored (nucleons) and 3-flavored (hyperons, strangeons, etc.) scenarios. The parameters are calibrated to reproduce the saturation properties of nuclear matter. The energy per baryon of strangeon matter is smaller than that of baryon matter if the strangeon carries a large number of valence quarks, which stiffens the equation of state and consequently increases the maximum mass of strangeon stars. The maximum mass and tidal deformability of strangeon stars within the present model are consistent with the observation, i.e. the maximum mass of strangeon stars can be $$sim$$2.5 solar mass, and the tidal deformability of a 1.4 solar mass star can be $$180lesssimLambdalesssim340$$.

論文

Unified nuclear matter equations of state constrained by the in-medium balance in density-dependent covariant density functionals

Xia, C.-J.*; Sun, B. Y.*; 丸山 敏毅; Lon, W.-H.*; Li, A.*

Physical Review C, 105(4), p.045803_1 - 045803_14, 2022/04

 被引用回数:5 パーセンタイル:92.41(Physics, Nuclear)

Assuming spherical and cylindrical approximations for the Wigner-Seitz cell, typical nuclear matter structures (droplet, rod, slab, tube, bubble, and uniform) are observed. We then investigate the equations of state and microscopic structures of nuclear matter with both fixed proton fractions and beta equilibration, where two covariant density functionals, DD-LZ1 and DD-ME2, are adopted. Despite the smaller slope $$L$$ of symmetry energy obtained with the functional DD-LZ1, the curvature parameter $$K_{rm sym}$$ is much larger than that of DD-ME2. Consequently, different mass-radius relations of neutron stars are predicted by the two functionals. Different microscopic structures of non-uniform nuclear matter are obtained as well, which are expected to affect various physical processes in neutron star properties and evolutions.

論文

Effects of three-baryon forces on kaon condensation in hyperon-mixed matter

武藤 巧*; 丸山 敏毅; 巽 敏隆*

Physics Letters B, 820, p.136587_1 - 136587_6, 2021/09

 被引用回数:2 パーセンタイル:66.58(Astronomy & Astrophysics)

相対論的平均場理論(RMF)の枠組みで$$sigma$$中間子場の非線形ポテンシャルを用いずに、バリオン間普遍3体斥力(UTBF、核子系ではTNRと略記)、及び核物質の飽和密度$$rho_0$$近傍で引力的に作用する核子3体力(TNA)を現象論的に導入し、対称核物質の飽和性と$$rho_0$$での非圧縮率、対称エネルギーの実験値を再現するように定めた。このような条件のもとでは、中性子物質のslope parameter $$L$$が高密度での状態方程式と強く関連していることが分かった。これを用いて(hyperon+$$K$$)相の状態方程式を求め、重い中性子星質量の観測と矛盾せずに、高密度星の内部構造を(hyperon+$$K$$)相を含むハドロン物質描像で説明できることを示した。

論文

Nuclear pasta structures and symmetry energy

Xia, C.-J.*; 丸山 敏毅; 安武 伸俊*; 巽 敏隆*; Zhang, Y.-X.*

Physical Review C, 103(5), p.055812_1 - 055812_13, 2021/05

 被引用回数:12 パーセンタイル:91.07(Physics, Nuclear)

In the framework of the relativistic mean field model with Thomas-Fermi approximation, we study the structures of low density nuclear matter in a three-dimensional geometry with reflection symmetry. The effect of finite cell size is treated carefully by searching for the optimum cell size. Typical pasta structures (droplet, rod, slab, tube, and bubble) arranged in various crystalline configurations are obtained for both fixed proton fractions and $$beta$$-equilibration. It is found that the properties of droplets/bubbles are similar in body-centered cubic (BCC) and face-centered cubic (FCC) lattices, where the FCC lattice generally becomes more stable than BCC lattice as density increases. For the rod/tube phases, the honeycomb lattice is always more stable than the simple one. By introducing an $$omega$$-$$rho$$ cross coupling term, we further examine the pasta structures with a smaller slope of symmetry energy $$L = 41$$ MeV, which predicts larger onset densities for core-crust transition and non spherical nuclei. Such a variation due to the reduction of $$L$$ is expected to have impacts on various properties in neutron stars, supernova dynamics, and binary neutron star mergers.

論文

Systematic study on the quark-hadron mixed phase in compact stars

Xia, C.-J.*; 丸山 敏毅; 安武 伸俊*; 巽 敏隆*; Shen, H.*; 富樫 甫*

Physical Review D, 102(2), p.023031_1 - 023031_18, 2020/07

 被引用回数:13 パーセンタイル:75.05(Astronomy & Astrophysics)

高密度星を構成する物質のクォーク-ハドロン混合相について調べる。クォーク相とハドロン相はそれぞれいくつかのモデルにより計算し、混合相の形状と状態方程式については、Ravenhallらによる連続的な幾何学的次元による計算法を踏襲する。その際表面張力は固定した値のものの他、多重反射展開法によるものと、equivparticle法によるものとを使う。これによって天体の全体的構造や質量,半径などが得られる。天体の半径と潮汐変形性の相関はハイブリッド星でも中性子星のときと同様であった。重い天体になると中心付近にクォーク物質が現れ、クォーク-ハドロンの境界の表面張力が全体の構造に対して重要になる。0.8fm$$^{-3}$$以下の密度では観測量により状態方程式に対する制限が良く得られるが、高密度では不定性が大きかった。

論文

Effects of universal three-body repulsion on kaon condensation in hyperonic matter

武藤 巧*; 丸山 敏毅; 巽 敏隆*; 高塚 龍之*

JPS Conference Proceedings (Internet), 26, p.024019_1 - 024019_4, 2019/11

The equation of state with coexistent phase of kaon condensation and hyperons [the ($$Y + K$$) phase] in highly dense matter is constructed so as to be consistent with the recent observations of massive neutron stars. The nonlinear effective chiral Lagrangian is combined with the relativistic mean-field theory. The universal three-body repulsive force is further introduced based on the string-junction model. It is shown that the stiff equation of state with the ($$Y + K$$) phase, leading to the maximum mass of neutron stars as large as two solar mass, can be obtained for the larger value of the range parameter of the repulsive core included in the string-junction model. Some problems to be resolved such as causality are mentioned.

論文

Hybrid equation of state with pasta phases, and third family of compact stars

Maslov, K.*; 安武 伸俊*; Blaschke, D.*; Ayriyan, A.*; Grigorian, H.*; 丸山 敏毅; 巽 敏隆*; Voskresensky, D. N.*

Physical Review C, 100(2), p.025802_1 - 025802_11, 2019/08

 被引用回数:42 パーセンタイル:97.36(Physics, Nuclear)

ハドロン-クォーク相転移に対するパスタ相の及ぼす影響を、相対論的平均場による状態方程式に関してしらべた。パスタ相の存在をフルに考慮した数値計算による状態方程式と従来の2相の内挿による混合相の状態方程式を比較した。ハドロン相・クォーク相双方に対して混合相の状態方程式がMaxwell構成法とほぼ一致する表面張力の限界値が得られた。そしてその値は理論による推定値とよく一致した。また、ベータ平衡な中性子星物質まで理論を拡張することで、ハイブリッド高密度星の構造と第3系列のロバストネスに対するパスタ相の影響を議論した。

論文

Multidimensional structure of chiral crystals in quark matter

Lee, T.-G.*; 安武 伸俊*; 丸山 敏毅; 巽 敏隆*

Proceedings of Science (Internet), 281, p.326_1 - 326_8, 2017/05

We discuss the possibility of a multidimensional structure of inhomogeneous chiral condensates, which might be realized in cold and dense quark matter or the core of compact stars. For one-dimensional structures, the system becomes unstable at finite temperature due to the Landau-Peierls instability attributed to the excitation of the Nambu-Goldstone modes, with the result that there is no long-range order, while quasi-long-range order is realized instead. On the other hand, chirally inhomogeneous phases with two- or three-dimensional modulations may be realized as a true long-range ordered phase at any temperature, as inferred from the Landau-Peierls theorem. We here consider possible strategies to explore a multidimensional structure of chiral crystals.

論文

Kaon condensation in hyperonic matter and equation of state

武藤 巧*; 丸山 敏毅; 巽 敏隆*

JPS Conference Proceedings (Internet), 14, p.020809_1 - 020809_3, 2017/02

 被引用回数:0 パーセンタイル:0.03

Kaon condensation in hyperon-mixed matter, which may be realized in neutron stars, is investigated on the basis of the relativistic mean-field theory for baryon-baryon interaction, combined with the effective chiral Lagrangian. We introduce the range terms for both nucleons and hyperons and a pole contribution from the $$Lambda$$(1405) so as to reproduce the $$S$$-wave on-shell $$KN$$ scattering lengths. Onset density of kaon condensation in the hyperon-mixed matter and the equation of state (EOS) is obtained. It is shown that coexistence of kaon condensation and hyperon-mixed matter necessarily leads to significant softening of the EOS. We address stiffening effects to make the EOS consistent with recent observations of massive neutron stars.

論文

Neutron star cooling with various superfluid and superconducting states

野田 常雄*; 橋本 正章*; 松尾 康秀*; 安武 伸俊*; 丸山 敏毅; 巽 敏隆*

JPS Conference Proceedings (Internet), 14, p.020805_1 - 020805_3, 2017/02

 被引用回数:0 パーセンタイル:0.03

A neutron star is a highly dense object which lasts after a supernova explosion. The density of a neutron star overcomes the nuclear density, and the temperature is high at the beginning of its history. An isolated neutron star does not have any heat sources, and it cools down emitting thermal energy by neutrinos. The neutrino emission process depends on the state of interior matter of the neutron star. To compare theoretical simulations and observations of neutron stars, it can constrain the nuclear theory of high density region. We create a model of neutron stars with colour superconducting quark matter and nucleon super fluidity / superconductivity, to satisfy recent observations, including two 2$$M$$$$_odot$$ neutron stars. We parameterize these super-states and demonstrate the cooling curves, which show heavy stars do not always cool faster than lighter stars.

論文

Multi-dimensional structure of crystalline chiral condensates in quark matter

Lee, T.-G.*; 西山 和也*; 安武 伸俊*; 丸山 敏毅; 巽 敏隆*

JPS Conference Proceedings (Internet), 14, p.020808_1 - 020808_3, 2017/02

 被引用回数:0 パーセンタイル:0.03

We explore the multi-dimensional structure of inhomogeneous chiral condensates in quark matter. For a one-dimensional structure, the system becomes unstable at finite temperature due to the Nambu-Goldstone excitations. However, inhomogeneous chiral condensates with multi-dimensional modulations may be realized as a true long-range order at any temperature, as inferred from the Landau Peierls theorem. We here present some possible strategies for searching the multi-dimensional structure of chiral crystals.

論文

Finite size effects in hadron-quark phase transition by the Dyson-Schwinger method

安武 伸俊*; Chen, H.*; 丸山 敏毅; 巽 敏隆*

Journal of Physics; Conference Series, 665(1), p.012068_1 - 012068_4, 2016/01

 被引用回数:6 パーセンタイル:88.76

We study the hadron-quark phase transition, taking into account the finite-size effects for neutron star matter. For the hadron phase, we adopt a realistic equation of state within the framework of the Brueckner-Hartree-Fock theory. For the quark phase, we apply the Dyson-Schwinger method. The properties of the mixed phase are clarified by considering the finite-size effects. We find that, if the surface tension is strong enough, the equation of state becomes to be close the one with the Maxwell condition, though we properly adopt the Gibbs conditions. This result is qualitatively the same with the one by the use of the simple bag model. We also find that the mass-radius relation by the EoS is consistent with the observations of massive neutron stars.

論文

Structure and properties of nuclear matter at the first-order phase transitions

丸山 敏毅

Acta Astronomica Sinica, 56(Suppl.), p.40 - 42, 2015/11

中性子星の中の核物質中で形成される非一様な構造の影響について論じた。核物質の一次相転移に伴う非一様な核物質に関しては広く研究されているが、中性子星の大域的構造に対する影響は小さいと言われてきた。しかし我々は非一様構造が物質の組成に与える影響の大きいことを強調したい。

論文

Cooling of compact stars with color superconducting quark matter

野田 常雄*; 安武 伸俊*; 橋本 正章*; 丸山 敏毅; 巽 敏隆*; 藤本 正行*

Acta Astronomica Sinica, 56(Suppl.), p.52 - 54, 2015/11

コンパクト星の冷却シナリオを示す。カシオペアA(Cas A)の観測により中央のソースは高い有効温度のコンパクト星で、エキゾチックな相を持たない場合の冷却と矛盾しない。Cas Aの観測データから、Cas Aの質量が太陽質量の1.5倍以上となることが分かる。それは重いコンパクト星ほど早く冷えるという現在のコンパクト星の冷却シナリオと矛盾する可能性がある。我々はコンパクト星の冷却にカラー超伝導のあるクォーク物質の効果を入れ、ギャップエネルギー$$Delta$$が10MeVより大きいと仮定した。冷却曲線を計算すると、重い星はゆっくり冷えて軽い星はその反対の傾向を持つことを示した。

論文

Coexistence of kaon condensation and hyperons in hadronic matter and its relevance to quark matter

武藤 巧*; 丸山 敏毅; 巽 敏隆*

Acta Astronomica Sinica, 56(Suppl.), p.43 - 45, 2015/11

中性子星において実現している可能性があるKaon凝縮とハイペロンの共存を、有効カイラルLagrangianを加えた相対論的平均場模型により調べた。Kaonの凝縮した相がハイペロンの混入した物質中に存在することは可能だが、物質の状態方程式の極端な軟化を招いてしまう。状態方程式を固くし最近の観測に合うようにするために必要な効果について論じる。

論文

Quark-hadron phase transition with finite-size effects in neutron stars

安武 伸俊*; Benic, S.*; Blaschke, D.*; 丸山 敏毅; 巽 敏隆*

Acta Astronomica Sinica, 56(Suppl.), p.85 - 87, 2015/11

中性子星におけるクォークーハドロン相転移について調べた。複数成分の系では、相転移の際に構造を持った混合相の有限サイズ効果を考慮する必要性がある。相転移はクォーク物質やハドロン物質のモデルに強く依存し、2相間の表面張力やニュートリノ含有率、温度にも依存する。しかし、モデルによらず表面張力が強いとMaxwell構成法の状態方程式に似たものになり、弱いとバルクなギブス条件のものになることが分かった。また、我々の提唱する状態方程式が与える天体の質量-半径曲線は、観測と矛盾しないことが分かった。

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